Added support of operational transformation

1 files changed, 117 insertions, 0 deletions

diff --git a/lib/ot/selection.js b/lib/ot/selection.js
new file mode 100644
index 00000000..72bf8bd6
--- /dev/null
+++ b/lib/ot/selection.js
@@ -0,0 +1,117 @@
+if (typeof ot === 'undefined') {
+  // Export for browsers
+  var ot = {};
+}
+
+ot.Selection = (function (global) {
+  'use strict';
+
+  var TextOperation = global.ot ? global.ot.TextOperation : require('./text-operation');
+
+  // Range has `anchor` and `head` properties, which are zero-based indices into
+  // the document. The `anchor` is the side of the selection that stays fixed,
+  // `head` is the side of the selection where the cursor is. When both are
+  // equal, the range represents a cursor.
+  function Range (anchor, head) {
+    this.anchor = anchor;
+    this.head = head;
+  }
+
+  Range.fromJSON = function (obj) {
+    return new Range(obj.anchor, obj.head);
+  };
+
+  Range.prototype.equals = function (other) {
+    return this.anchor === other.anchor && this.head === other.head;
+  };
+
+  Range.prototype.isEmpty = function () {
+    return this.anchor === this.head;
+  };
+
+  Range.prototype.transform = function (other) {
+    function transformIndex (index) {
+      var newIndex = index;
+      var ops = other.ops;
+      for (var i = 0, l = other.ops.length; i < l; i++) {
+        if (TextOperation.isRetain(ops[i])) {
+          index -= ops[i];
+        } else if (TextOperation.isInsert(ops[i])) {
+          newIndex += ops[i].length;
+        } else {
+          newIndex -= Math.min(index, -ops[i]);
+          index += ops[i];
+        }
+        if (index < 0) { break; }
+      }
+      return newIndex;
+    }
+
+    var newAnchor = transformIndex(this.anchor);
+    if (this.anchor === this.head) {
+      return new Range(newAnchor, newAnchor);
+    }
+    return new Range(newAnchor, transformIndex(this.head));
+  };
+
+  // A selection is basically an array of ranges. Every range represents a real
+  // selection or a cursor in the document (when the start position equals the
+  // end position of the range). The array must not be empty.
+  function Selection (ranges) {
+    this.ranges = ranges || [];
+  }
+
+  Selection.Range = Range;
+
+  // Convenience method for creating selections only containing a single cursor
+  // and no real selection range.
+  Selection.createCursor = function (position) {
+    return new Selection([new Range(position, position)]);
+  };
+
+  Selection.fromJSON = function (obj) {
+    var objRanges = obj.ranges || obj;
+    for (var i = 0, ranges = []; i < objRanges.length; i++) {
+      ranges[i] = Range.fromJSON(objRanges[i]);
+    }
+    return new Selection(ranges);
+  };
+
+  Selection.prototype.equals = function (other) {
+    if (this.position !== other.position) { return false; }
+    if (this.ranges.length !== other.ranges.length) { return false; }
+    // FIXME: Sort ranges before comparing them?
+    for (var i = 0; i < this.ranges.length; i++) {
+      if (!this.ranges[i].equals(other.ranges[i])) { return false; }
+    }
+    return true;
+  };
+
+  Selection.prototype.somethingSelected = function () {
+    for (var i = 0; i < this.ranges.length; i++) {
+      if (!this.ranges[i].isEmpty()) { return true; }
+    }
+    return false;
+  };
+
+  // Return the more current selection information.
+  Selection.prototype.compose = function (other) {
+    return other;
+  };
+
+  // Update the selection with respect to an operation.
+  Selection.prototype.transform = function (other) {
+    for (var i = 0, newRanges = []; i < this.ranges.length; i++) {
+      newRanges[i] = this.ranges[i].transform(other);
+    }
+    return new Selection(newRanges);
+  };
+
+  return Selection;
+
+}(this));
+
+// Export for CommonJS
+if (typeof module === 'object') {
+  module.exports = ot.Selection;
+}